This project involves the development and dissemination of a method for measuring abstract qualities important to aging research and theory construction such as depression, life-satisfaction, morale, wisdom, and expertise in ways that are appropriately different for different individuals or age groups while holding constant the meaning of those qualities being assessed. Rigorous mathematical concepts of invariance will be employed while accommodating idiosyncratic features of individuals and of subgroups that differ by variables such as age. Rules for meeting these conditions with mathematical rigor will be developed and described and the procedures will be illustrated with extant data. How the evaluation of psychometric properties such as reliability, convergent and discriminant validity, etc., can be accomplished within the novel measurement framework will be described and implications of the approach for improving particular assessment instruments (e.g., the CES-D) and creating new ones for use in studies of aging will be examined and discussed. Benefits to accrue include the development of improved assessment devices that can be used in a wide range of research projects, including individual data collections, clinical trials, and epidemiological studies. PUBLIC HEALTH RELEVANCE: Completion of this project will lead to more appropriate measuring devices by which important attributes such as depression, morale, and life-satisfaction can be measured by physicians, counselors, and researchers. The results can then be used for more effective diagnosis, selection, and classification procedures in dealing with both well and impaired individuals, including the frail elderly.